recap sesame astronomy 2011 week 8 sesame astronomy 2011 week 8
Post on 20-Dec-2015
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What we’ve covered
The cause of the seasons
The cause of the moon phases
The solar system
The Sun
Stars
The Cause of the SeasonsEarth orbits Sun
Earth’s rotation axis is tilted relative to orbit
at one side of orbit Northern hemisphere is tilted toward sun, 6 months later Northern hemisphere is tilted away from sun
Tilted toward: longer days, sun higher in sky (direct/concetrated sunlight), tilted away: shorter days, sun lower in sky (indirect/watered down sunlight)
Cause of moon phases
moon orbits earth
exactly half of moon (side facing sun) is always illuminated
relative position of earth-moon-sun determines phase
different phases rise/set at different “times” of day (know which phases rise/set/are highest at which times)
What’s in solar systemSun at center, planets orbit it
inner planets are rocky, outer planets are gaseous (why?)
in between Mars and Jupiter is asteroid belt
outside orbit of Neptune are Kuiper belt and Oort cloud
The solar system
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
Which planets have moons?
Be able to say one unique thing about each planet
FormationStarted as large gas cloud VERY SLOWLY rotating
collapsed, heated up, spin sped up, became a disk
small clumps grew into bigger clumps, which grew into planets
planets “cleared their orbits” either accreted or kicked out all debris/gas/dust
center of cloud became the sun
The Sunour starfuses H → He in coredifferential rotation: at poles rotation period is 33 days, at equator it’s 25 dayssunspots caused by magnetic fields poking through “surface”sunspot cycle: few sunspots at mid-lattitudes → lots of sunspots at equator → field flips and cycle starts againfield poking through surface → sunspots, prominences, and flares
Coming up:Planetarium trip: THIS SUNDAY 2pm
Homework from chapters
Take-home “final” - pick up Week 10
Sun project - turn in Week 10
Moon project - turn in Week 10
Stellar livesStars can have masses in the range 0.08M⊙ - 120 M⊙ (why this range?)
Mass determines temperature, which determines color and lifetime
MANY MORE low-mass stars (M < 8-10M⊙) than high-mass (M > 8-10M⊙)
Stellar deaths: low-massrun out of H in core, core shrinks and heats up: expands outer layers into Red Giant, ignites H-shell fusion, (eventually) ignites He-core fusion
He in core runs out, core shrinks, expands outer layers, pushes them off (they are a planetary nebula)
VERY HOT CO core is white dwarf, cools slowly
Stellar deaths: high massruns out of H in core, core shrinks and heats up, ignites He fusion in core and H-shell fusion around core
runs out of He in core, core shrinks and heats up, ignites He-shell fusion and C core fusion
runs out of C in core, core shrinks and heats up... until core is made of iron
(can’t get energy out of iron - why not?)
Stellar deaths: high mass
iron shrinks and heats up, breaks into He nuclei
He nuclei break into P’s and n’s (still shrinking)
e’s and p’s get squeezed into n’s (still shrinking)
core is now just neutrons and outer layers begin to collapse
shrinking core caused fusion shells to expand - outer layers hit expanding fusion shells and explode
Stellar deaths
high-mass stars ALWAYS end in a Type II Supernova -> make lots of “alpha elements”
low-mass stars COULD become a Type Ia Supernva under the right conditions (what are they?) -> make lots of iron
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